The invention relates to an arrangement and a method for stabilizing a voltage applied to a first electric consuming device arranged in an onboard power supply system of a vehicle. In addition to at least one first consuming device, the onboard power supply system also has at least one second electric consuming device and a first voltage supply unit which provides a supply voltage.
To a high degree, vehicles are nowadays equipped with electric components. This ranges from simple mechanisms, such as fans, seat heaters or rear window heaters, to highly complex control systems by which a quantity representing the driving dynamics of the vehicle can be controlled or influenced. Examples of such control systems are systems already being used today for influencing the chassis of a vehicle or systems for controlling the yaw rate of a vehicle. However, systems, such as brake-by-wire or steer-by-wire systems, which can be used in the future, should also be mentioned.
For activating or for maintaining the activation, these electric components have to be supplied with an electric voltage and thereby with electric energy. In this case, it is important that the onboard power supply voltage provided for this purpose is stable over time or is maintained in a stable state, mainly with a view to electrical components which should be classified as being voltage-sensitive. A component is voltage-sensitive if a malfunctioning or function impairment of this component occurring during the driving operation of the vehicle and caused by an instability of the onboard power supply voltage has the result that the driving operation can no longer be maintained unrestrictedly or represents a danger potential for further driving operation. Whereas, with respect to electrical components which are to be classified as non-voltage-sensitive, instabilities in the onboard power supply voltage are less problematic or not problematic at all.
However, especially in the driving operation of a vehicle, there are operations during which fluctuations in the onboard power supply voltage may occur, for example, caused by voltage drops on loads, parasitic resistances or caused by a very high current demand of an electric consuming device. Particularly in the case of vehicles equipped with a so-called automatic start-stop system, instabilities may occur in the onboard power supply voltage when the internal-combustion engine is restarted. In this case, it is unimportant whether a conventional vehicle is involved that is driven exclusively by an internal-combustion engine, or a hybrid vehicle in which an internal-combustion engine as well as an electric machine are provided for the propulsion. Measures for stabilizing the onboard power supply voltage generally have to be taken in the case of hybrid vehicles, particularly vehicles constructed as parallel hybrids.
Instabilities in the onboard power supply voltage may occur mainly when the electric motor is additionally started. In this case, the hybrid vehicle is in an operating state in which it is driven solely by the electric machine, and the internal-combustion engine is started for generating the torque required for the propulsion, instead of the electric machine.
Especially with a view to electrical components that are starting-voltage-sensitive, an onboard supply voltage with a behavior that is stable over time is therefore particularly important. Starting-voltage-sensitive components are those components which react with function impairments or malfunctioning to the considerable onboard power supply voltages that may occur when restarting or additionally starting an internal-combustion engine. This may also involve those components which are relevant to the driving operation of the vehicle during or immediately following a restarting or additional starting operation.
Various measures are known for stabilizing the onboard power supply voltage or for providing a stable onboard power supply voltage. Thus, so-called high-voltage or low-voltage starting systems may be used, which permit the restarting or additional starting of an internal-combustion engine without the occurrence of instabilities in the onboard power supply voltage. Low-voltage starting systems can be used in conventional vehicles as well as in hybrid vehicles.
A vehicle equipped with a low-voltage starting system, in addition to the conventional basic onboard power supply system, has a further starting onboard power supply system which is coupled with the basic onboard power supply system by way of a coupling element, for example, a voltage transformer or a switch. The starting onboard power supply system, which has a separate battery, provides electric energy required for the restarting or additional starting of the internal-combustion engine, while the remaining electrical components installed in the vehicle are supplied by way of the basic onboard power supply system.
The disadvantage of this implementation is that an additional onboard power supply system, specifically the starting onboard power supply system is needed. On the one hand, this results in high costs caused by the components of the starting onboard power supply system itself and by the components required for the coupling of the two power supply systems. On the other hand, the accommodation of the additional components of the starting onboard power supply system is not unproblematic because limited space is available in a vehicle.
High-voltage starting systems are used in the case of hybrid vehicles constructed as parallel hybrids. In the case of such a vehicle, the internal-combustion engine and the electric machine are, as a rule, connected with one another and with the transmission by way of a clutch unit. On the one hand, it thereby becomes possible that the vehicle can be driven solely by the internal-combustion engine or solely by the electric machine or, in a combined manner by both. On the other hand, it is conceivable to implement a restarting or additional starting of the internal-combustion engine while using the electric machine.
This implementation has the disadvantage that the electric machine provided for the driving operation and also the electric accumulator, by which the electric machine is supplied with electric energy, have to have larger dimensions than would actually be necessary because, in addition to the torque causing the vehicle propulsion, it also has to provide a torque causing the restarting or additional starting of the internal-combustion engine. This results in higher costs.
It is therefore an object of the present invention to further develop an arrangement and a method of the above-mentioned type in order to be able to implement the stabilization of a voltage applied to a first electric consuming device arranged in an onboard power supply system of a vehicle, without having to use additional or larger-dimensioned components for this purpose or without having to provide a larger space. An arrangement and a corresponding method, respectively, are to be provided, which are cost-effective and easy to operate.
This and other objects are achieved by an arrangement for stabilizing a voltage applied to a first electric consuming device arranged in an onboard power supply system of a vehicle, the onboard power supply system also having at least one second electric consuming device and a first voltage supply unit which provides a supply voltage. The arrangement includes a storage unit constructed for storing electric energy at least temporarily, a second voltage supply unit for providing a charging voltage, a switching unit to which at least the first electric consuming device, the storage unit, the first voltage supply unit and the second voltage supply unit are connected, and a control unit which is constructed for determining whether a stabilization of the voltage applied to the first electric consuming device is to be carried out. The control unit is further constructed, as long as a stabilization is not to be carried out, for activating the switching unit such that the first electric consuming device is connected to the first voltage supply unit and, as soon as a stabilization is to be carried out, for activating the switching unit such that the first electric consuming device is connected to a series connection formed by the storage unit and the first voltage supply unit. The control unit is still further constructed for, subsequently to an implemented stabilization, in each case, at least temporarily activating the second voltage supply unit, the second electric consuming device and the switching unit such that the second voltage supply unit provides a charging voltage whose value is greater than the supply voltage provided by the first voltage supply unit, an electric current flows at least temporarily through the second electric consuming device, and a charging of the storage unit becomes possible by way of a current path formed by the second voltage supply unit and the second electric consuming device.
The object is also achieved by a method in which the following steps are implemented in a control unit:
(a) determining whether a stabilization of the voltage applied to the first electric consuming device is to be carried out;
(b) activating the switching unit as long as a stabilization is not to be carried out, such that the first electric consuming device is connected to the first voltage supply unit;
(c) activating the switching unit as soon as a stabilization is to be carried out, such that the first electric consuming device is connected to a series connection formed by the storage unit and the first voltage supply unit; and
(d) activating the second voltage supply unit, the second electric consuming device and the switching unit subsequently to an implemented stabilization, in each case, at least temporarily such that: the second voltage supply unit provides a charging voltage whose value is greater than the supply voltage provided by the first voltage supply unit, an electric current flows through the second electric consuming device at least temporarily, and a charging of the storage unit becomes possible by way of a current path formed by the second voltage supply unit and the second electric consuming device.
The arrangement according to the invention and the method according to the invention are based on the following. On the one hand, a storage unit is provided which provides the energy that is required for the stabilization of the voltage applied to the first electric consuming device. On the other hand, a differentiation with respect to the electric consuming devices takes place between first and second consuming devices. The first consuming devices are those consuming devices that are voltage-sensitive and therefore should be supplied with a stabilized supply voltage. The second consuming devices are non-voltage-sensitive consuming devices which can be operated also with a non-stabilized supply voltage. The stabilization of the supply voltage required for the operation of the first consuming devices is achieved in that, if required, an additional storage unit is connected in series with the original voltage supply unit. As a result, during an operating state of the vehicle in which an increased energy demand is required for operating one or more electric consuming devices installed in the vehicle and which would actually lead to an unstable supply voltage, the electric energy stored in the storage unit can be used for stabilizing the supply voltage. The charging of the storage unit necessary after the stabilization has taken place is implemented by way of a second voltage supply unit and the second electric consuming device, which are both installed in the vehicle anyhow. Additional or larger-dimensioned components or even a charging circuit, which also is a fairly large component, provided specifically for the charging of the storage unit, will not be necessary. No additional installation space therefore has to be made available. On the whole, an arrangement and a corresponding method are provided which are cost-effective and easy to operate.
The above-mentioned task has therefore been achieved in its entirety.
As far as the activating of the second voltage supply unit, the second electric consuming device and the switching unit, is concerned, which takes place subsequently to the stabilization of the voltage applied to the first consuming device, the following is pointed out. It is therefore not absolutely necessary for the second voltage supply unit and the second electric consuming device to be activated such that the second voltage supply unit provides the increased charging voltage for a certain time period and, in the process, simultaneously the second electric consuming device is constantly activated with respect to the current flow. It is theoretically sufficient to activate solely the second voltage supply unit for providing the increased charging voltage without simultaneously activating the second electric consuming device. However, since a major voltage drop occurs at the storage unit when the second electric consuming device is activated such that current will flow through it, the second electric consuming device will be activated at least temporarily during the time period in which the second voltage supply unit provides the increased charging voltage.
The present invention is consequently used in a vehicle which has an internal-combustion engine and a first electric machine. The first electric machine is constructed for driving the internal-combustion engine at least temporarily. The control unit is further constructed, in order to determine whether a stabilization of the voltage applied to the first electric consuming device is to be carried out, for evaluating whether a restarting and/or an additional starting of the internal-combustion engine is to be implemented by the first electric machine. A large amount of electric energy is required especially for the restarting of an internal-combustion engine (vehicle with an automatic start-stop system) and for the additional starting of an internal-combustion engine (hybrid vehicle). When this amount of energy is taken from the voltage supply unit, which provides the supply voltage of the onboard power supply system, this results in a clear reduction of the supply voltage. This instability would lead to impairments of functions, or malfunctioning, in the case of the first consuming device (voltage-sensitive consuming device). Consequently, during the restarting or additional starting of the internal-combustion engine, the first consuming device is connected to a series connection formed by the first voltage supply unit and the storage unit and is supplied with voltage or electric energy by it.
As mentioned above, the first consuming device is a voltage-sensitive, particularly a starting-voltage-sensitive, consuming device. This may, for example, be a consuming device that is relevant to the driving operation. If a malfunctioning or function impairment were to occur in the case of such a consuming device, this could have the result that the driving operation can no longer be maintained in an unrestricted manner or this represents a danger potential for the further driving operation. Such a consuming device may, for example, be a system for controlling the yaw rate of the vehicle, a chassis control system, a steer-by-wire system, a brake-by-wire system or the like. The second consuming device advantageously is a non-voltage-sensitive, particularly a non-starting-voltage-sensitive, consuming device. This may, for example, be a consuming device that is not relevant to the driving operation. If a malfunctioning or function impairment were to occur in the case of such a consuming device, an unrestricted driving operation of the vehicle would nevertheless be possible. This may, for example, be a rear window heater, a seat heater, a fan, a blower or the like.
In a further development of the invention, a restarting of the internal-combustion engine that is to be carried out is detected when a start-driving signal is present in an idle state of the vehicle, in which case, in the idle state of the vehicle, the vehicle is stationary and the internal-combustion engine has stopped or has a rotational engine speed that is between a rotational shut-off speed and the zero value, and/or an additional starting of the internal-combustion engine is detected when, in a moving state of the vehicle, an engine torque demand is present, in which case, in the vehicle moving state, the vehicle is driving and the internal-combustion engine has stopped or has a rotational engine speed that is between a rotational shut-off speed and the zero value.
During the restarting as well as during the additional starting, an operative connection of the internal-combustion engine with the driven wheels of the vehicle is immediately imminent. The idle state of the vehicle as well as the moving state of the vehicle are focused on the fact that the internal-combustion engine is either at a standstill (zero engine rotational speed) or is carrying out a diminishing rotational movement (the engine rotational speed is between the shut-off rotational speed and the zero value). In the idle state of the vehicle, the vehicle speed should be zero, whereas, in the moving state of the vehicle, the rotational speed has a value different from zero.
The driving-start signal represents an immediate imminent driving start of the vehicle which is to begin from the idle state of the vehicle. Preferably, this should be a driving start initiated by the driver of the vehicle. A signal that represents the actuating of the clutch pedal by the driver can, for example, be used as the driving start signal. However, as an alternative, it may also be an automated driving start, thus a driving start initiated independently of the driver.
The engine torque demand represents a torque which is to be set by the internal-combustion engine in the present vehicle moving state dependent on the driver or independent of the driver. A torque to be set in a manner dependent on the driver is obtained, for example, by an actuation of the accelerator pedal by the driver. Consequently, in this case, the engine torque demand may be a quantity representing the accelerator pedal actuation. A longitudinal control system, for example, can generate an engine torque demand that is independent of the driver, the longitudinal control system being, for example, an adaptive cruise control system.
The shut-off rotational speed is that rotational engine speed of the internal-combustion engine which occurs during the dropping of the internal-combustion engine, i.e. during or immediately after the interruption of the operative connection to the driven wheels, for example, caused by the actuation of the clutch. In the first moment, the shut-off rotational speed can correspond to the rotational idling speed; depending on the operation, however, it may temporarily definitely also be above the rotational idling speed.
The restarting and additional starting of the internal-combustion engine differs from the initial starting of the internal-combustion engine, which is triggered for the first time by the driver after entering the vehicle at the beginning of a trip. During the initial starting, it is not necessary that the internal-combustion engine provides a defined large torque within a minimal time period. Whereas, during the restarting, for example, at a traffic light, a large torque has to be provided by the internal-combustion engine within a very short time. A corresponding situation exists during the additional starting of the internal-combustion engine in a vehicle moving state. In this case, the internal-combustion engine has to provide a torque correlating with the vehicle moving state within a very short time.
In a further development of the invention, the switching unit has a first switching element and a second switching element. The two switching elements are preferably arranged as a parallel connection, so that the switching unit can advantageously take up two different switching states. Specifically, a first switching state which is taken up in the case of a restarting and/or additional starting of the internal-combustion engine to be carried out and in which the first electric consuming device is connected to the series connection formed by the storage unit and the first voltage supply unit; and a second switching state which is otherwise taken up and in which the first electric consuming device solely is connected to the first voltage supply unit. After the restarting and/or additional starting has taken place, the switching unit is advantageously controlled such that it maintains the first switching state. The two switching elements are preferably implemented as MOSFET transistors.
In a further development of the invention, the storage unit is constructed as a capacitor, particularly as a supercapacitor. In comparison to batteries, capacitors are distinguished by the fact that they can be charged by means of simpler charging methods and clearly more rapidly, which increases the availability of the supplied device or system. In addition, they have a longer service life and also a higher power density. Supercapacitors are constructed as double-layer capacitors. These are the capacitors with the highest energy density. The high capacity of supercapacitors is based on the fact that ions dissociate in a liquid electrolyte and thereby form a dielectric which has a thickness of a few atomic layers and a large electrode surface.
In a further development of the invention, the second electric consuming device is connected to the first voltage supply unit. The second electric consuming device is a non-voltage-sensitive or non-starting-voltage-sensitive consuming device. This consuming device therefore does not absolutely have to be supplied with a stabilized voltage. It is therefore also not necessary to supply it even only temporarily by way of the series connection formed by the storage unit and the first voltage supply unit. It can be connected directly, i.e. without an intermediately connected switching element, with the first voltage supply unit. As a result, it is possible at any time to operate the second consuming device and to charge the storage unit by means of the current flowing through it.
The invention is advantageously used in a hybrid vehicle constructed as a parallel hybrid. The vehicle therefore has a second electric machine which is constructed for, alone or in combination with the internal-combustion engine, driving the driven wheels of the vehicle. In this case, the second voltage supply unit is a voltage transformer which is connected on the input side with a switching circuit containing the second electric machine. Since, in the case of a hybrid vehicle, the second electric machine is supplied with electric energy, a hybrid vehicle necessarily has a second storage unit constructed especially for this purpose and also arranged in the switching circuit. The voltage transformer can therefore be supplied either by way of the storage unit or by way of the second electric machine, whereby the demand-dependent providing of a charging voltage is ensured by the voltage transformer.
If, in contrast, the vehicle is constructed as a conventional vehicle, the second voltage supply unit advantageously is a generator present in the vehicle. Therefore, the demand-dependent providing of a charging voltage is also ensured in this case. In the case of a conventional vehicle, it is necessary to charge the storage unit after a restarting of the internal-combustion engine has taken place. Since the internal-combustion engine is running after a restarting, the generator is driven and a charging voltage required for the charging of the storage unit is therefore available.
In a further development of the invention, the control unit is further developed for evaluating a driver entrance signal and for initially charging the storage unit when a driver entrance is detected. This measure has the advantage that the storage unit is charged already during the startup operations of the vehicle or at the beginning of the drive, and, if required, a stabilization can thereby take place of the voltage applied to the first electric consuming device. The driver entrance is detected, for example, as a result of the actuation of the vehicle locking system by the driver or by detecting a signal permitting the entrance, as used for keyless entrance systems. As an alternative, instead of the driver entrance, the ignition actuation can be used as a triggering criterion for the initial charging.
For not having to use additional components for the stabilization of the voltage applied to the first electric consuming device and therefore not requiring additional space and additional costs, components already present in the vehicle are preferably used for implementing the arrangement according to the invention. Thus, the first electric machine advantageously is a starter present in the vehicle, and the first voltage supply unit is an onboard power supply system battery present in the vehicle.
It is understood that the above-mentioned characteristics, which will be explained in the following, can not only be used in the respectively indicated combinations but also in other combinations or alone without leaving the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.